Hundreds of schools in England are staging a boycott of one of the cornerstones of primary education, the national schools tests, known as Sats.
About 600,000 10 and 11-year-olds are due to take the tests from Monday.
But heads and deputies from two big unions voted for a boycott.
BBC News has contacted 113 councils and found that - among those who responded - 15% of schools are not doing the tests.
The data is not complete, but the councils which have given information cover 73% of England's 17,000 primary schools.
Among the schools of which the BBC has details, nearly 1,900 (15%) say they will boycott the tests and about 5,650 say they will not (45%).
The councils say they do not know the situation in the remaining 40% of schools.